Brazilian results on structural masonry concrete blocks

The purpose of this paper is to study the mechanical behavior of concrete blocks and prisms when performing axial compression tests within the Brazilian base of knowledge, intending to foment data of this kind for a world-based network. The blocks were built using five different mixtures in which the quantity of cement and the compacting ratio (density) were varied (during the fabrication process). The three-course-high prisms were assembled using 1 cm (0.39 in.) thick full-bedded joints, always trying to leave the mortar's characteristics constant. The axial compression tests were conducted according to Brazilian practice code recommendations, because most of these standards are very similar to international practice codes. The compressive strength, strains, and rupture form of each mixture studied were recorded. Attempts were made to correlate the strength, efficiency ratio (block strength/prism strength) of the prisms, strains, and rupture form; with the quantity of cement and compacting ratio. The data are presented in tables and figures, and the obtained results are discussed throughout the text. Copyright © 2007, American Concrete Institute. All rights reserved.

Evaluation of perforated steel plates as connection in glulam-concrete composite structures

This paper shows the results of an experimental investigation carried out on a connection element of glulam and concrete composite structures, through double-sided push-out shear tests. The connection system was composed of perforated steel plates glued with epoxy adhesive. Five specimens were made and tested under shear forces. This innovative connection system showed an average initial slip modulus equivalent to 339.4 kN/mm. In addition, the connection system was evaluated by means of numerical simulations and the software ANSYS was used for this purpose. The numerical simulations demonstrated good agreement with the experimental data, especially in the regime of elastic-linear behavior of materials. (C) 2011 Elsevier Ltd. All rights reserved.

Materiali Compositi a Matrice Cementizia per i Rinforzi Strutturali

L’utilizzo degli FRP (Fiber Reinforced Polymer) nel campo dell’ingegneria civile riguarda essenzialmente il settore del restauro delle strutture degradate o danneggiate e quello dell’adeguamento statico delle strutture edificate in zona sismica; in questi settori è evidente la difficoltà operativa alla quale si va in contro se si volessero utilizzare tecniche di intervento che sfruttano materiali tradizionali. I motivi per cui è opportuno intervenire con sistemi compositi fibrosi sono: • l’estrema leggerezza del rinforzo, da cui ne deriva un incremento pressoché nullo delle masse sismiche ed allo stesso tempo un considerevole aumento della duttilità strutturale; • messa in opera senza l’ausilio di particolari attrezzature da un numero limitato di operatori, da cui un minore costo della mano d’opera; • posizionamento in tempi brevi e spesso senza interrompere l’esercizio della struttura. Il parametro principale che definisce le caratteristiche di un rinforzo fibroso non è la resistenza a trazione, che risulta essere ben al di sopra dei tassi di lavoro cui sono soggette le fibre, bensì il modulo elastico, di fatti, più tale valore è elevato maggiore sarà il contributo irrigidente che il rinforzo potrà fornire all’elemento strutturale sul quale è applicato. Generalmente per il rinforzo di strutture in c.a. si preferiscono fibre sia con resistenza a trazione medio-alta (>2000 MPa) che con modulo elastico medio-alto (E=170-250 GPa), mentre per il recupero degli edifici in muratura o con struttura in legno si scelgono fibre con modulo di elasticità più basso (E≤80 GPa) tipo quelle aramidiche che meglio si accordano con la rigidezza propria del supporto rinforzato. In questo contesto, ormai ampliamente ben disposto nei confronti dei compositi, si affacciano ora nuove generazioni di rinforzi. A gli ormai “classici” FRP, realizzati con fibre di carbonio o fibre di vetro accoppiate a matrici organiche (resine epossidiche), si affiancano gli FRCM (Fiber Reinforced Cementitious Matrix), i TRM (Textile Reinforced Mortars) e gli SRG (Steel Reinforced Grout) che sfruttano sia le eccezionali proprietà di fibre di nuova concezione come quelle in PBO (Poliparafenilenbenzobisoxazolo), sia un materiale come l’acciaio, che, per quanto comune nel campo dell’edilizia, viene caratterizzato da lavorazioni innovative che ne migliorano le prestazioni meccaniche. Tutte queste nuove tipologie di compositi, nonostante siano state annoverate con nomenclature così differenti, sono però accomunate dell’elemento che ne permette il funzionamento e l’adesione al supporto: la matrice cementizia

Longitudinal bar buckling behavior

Reinforced concrete columns might fail because of buckling of the longitudinal reinforcing bar when exposed to earthquake motions. Depending on the hoop stiffness and the length-over-diameter ratio, the instability can be local (in between two subsequent hoops) or global (the buckling length comprises several hoop spacings). To get insight into the topic, an extensive literary research of 19 existing models has been carried out including different approaches and assumptions which yield different results. Finite element fiberanalysis was carried out to study the local buckling behavior with varying length-over-diameter and initial imperfection-over-diameter ratios. The comparison of the analytical results with some experimental results shows good agreement before the post buckling behavior undergoes large deformation. Furthermore, different global buckling analysis cases were run considering the influence of different parameters; for certain hoop stiffnesses and length-over-diameter ratios local buckling was encountered. A parametric study yields an adimensional critical stress in function of a stiffness ratio characterized by the reinforcement configuration. Colonne in cemento armato possono collassare per via dell’instabilità dell’armatura longitudinale se sottoposte all’azione di un sisma. In funzione della rigidezza dei ferri trasversali e del rapporto lunghezza d’inflessione-diametro, l’instabilità può essere locale (fra due staffe adiacenti) o globale (la lunghezza d’instabilità comprende alcune staffe). Per introdurre alla materia, è proposta un’esauriente ricerca bibliografica di 19 modelli esistenti che include approcci e ipotesi differenti che portano a risultati distinti. Tramite un’analisi a fibre e elementi finiti si è studiata l’instabilità locale con vari rapporti lunghezza d’inflessione-diametro e imperfezione iniziale-diametro. Il confronto dei risultati analitici con quelli sperimentali mostra una buona coincidenza fino al raggiungimento di grandi spostamenti. Inoltre, il caso d’instabilità globale è stato simulato valutando l’influenza di vari parametri; per certe configurazioni di rigidezza delle staffe e lunghezza d’inflessione-diametro si hanno ottenuto casi di instabilità locale. Uno studio parametrico ha permesso di ottenere un carico critico adimensionale in funzione del rapporto di rigidezza dato dalle caratteristiche dell’armatura.

Prove di caratterizzazione meccanica del legame di adesione fra FRP ed acciaio

Il progresso nella tecnica di recupero e di rinforzo nelle strutture metalliche con i polimeri fibro-rinforzati FRP (fibre reinforced polymers). 1.1 Introduzione nelle problematiche ricorrenti delle strutture metalliche. Le strutture moderne di una certa importanza, come i grattacieli o i ponti, hanno tempi e costi di costruzione molto elevati ed è allora di importanza fondamentale la loro durabilità, cioè la lunga vita utile e i bassi costi di manutenzione; manutenzione intesa anche come modo di restare a livelli prestazionali predefiniti. La definizione delle prestazioni comprende la capacità portante, la durabilità, la funzionalità e l’aspetto estetico. Se il livello prestazionale diventa troppo basso, diventa allora necessario intervenire per ripristinare le caratteristiche iniziali della struttura. Strutture con una lunga vita utile, come per la maggior parte delle strutture civili ed edilizie, dovranno soddisfare esigenze nuove o modificate: i mezzi di trasporto ad esempio sono diventati più pesanti e più diffusi, la velocità dei veicoli al giorno d'oggi è aumentata e ciò comporta anche maggiori carichi di tipo dinamico.

Sul rinforzo di elementi in C.A.: confronto tra varie normative

Il documento pre-normativo italiano sul rinforzo di strutture in c.a. mediante l’uso di materiale fibrorinforzato. 1.1 INTRODUZIONE La situazione unica dell’Italia per quanto riguarda la conservazione delle costruzioni esistenti, è il risultato della combinazione di due aspetti, come primo, il medio-alto rischio sismico di una gran parte di territorio, come testimoniato dalla zonizzazione sismica recente, e come secondo aspetto, l'estrema complessità di un ambiente edilizio che non ha confronto nel mondo. Le tipologie della costruzione in Italia si distinguono a quelle stimate come patrimonio storico, che in alcuni casi risalgono a circa 2000 anni fa, a quelle che sono state costruite in ultimi cinque secoli, durante e dopo il Rinascimento, che sono considerate come patrimonio culturale ed architettonico dell' Italia (e del mondo!), infine a quelle fatte in tempi recenti, considerevolmente durante e dopo il boom economico del l960 ed ora visti come antiquate. Le due prime categorie in gran parte sono composte dalle edilizie di muratura, mentre agli ultimi principalmente appartengono le costruzioni di cemento armato.

Comportamiento estructural de elementos de fábrica reforzados con materiales compuestos avanzados solicitados a flexión y flexocompresión

El refuerzo de estructuras existentes mediante el encolado exterior de láminas de polímeros reforzados con fibras (FRP) se ha convertido en la aplicación más común de los materiales compuestos avanzados en construcción. Estos materiales presentan muchas ventajas frente a los materiales convencionales (sin corrosión, ligeros, de fácil aplicación, etc.). Pero a pesar de las numerosas investigaciones realizadas, aún persisten ciertas dudas sobre algunos aspectos de su comportamiento y las aplicaciones prácticas se llevan a cabo sólo con la ayuda de guías, sin que haya una normativa oficial. El objetivo de este trabajo es incrementar el conocimiento sobre esta técnica de refuerzo, y más concretamente, sobre el refuerzo a flexión de estructuras de fábrica. Con frecuencia el elemento reforzado es de hormigón armado y las láminas de FRP encoladas al exterior sirven para mejorar su resistencia a flexión, cortante o compresión (encamisados). Sin embargo su empleo en otros materiales como las estructuras de fábrica resulta muy prometedor. Las fábricas se caracterizan por soportar muy bien los esfuerzos de compresión pero bastante mal los de tracción. Adherir láminas de materiales compuestos puede servir para mejorar la capacidad resistente de elementos de fábrica sometidos a esfuerzos de flexión. Pero para ello, debe quedar garantizada una correcta adherencia entre el FRP y la fábrica, especialmente en edificios antiguos cuya superficie puede estar deteriorada por encontrarse a la intemperie o por el propio paso del tiempo. En el capítulo II se describen los objetivos fundamentales del trabajo y el método seguido. En el capítulo III se hace una amplia revisión del estado de conocimiento sobre el tema. En el apartado III.1 se detallan las principales características y propiedades mecánicas de fibras, matrices y materiales compuestos así como sus principales aplicaciones, haciendo especial hincapié en aspectos relativos a su durabilidad. En el apartado III.2 se incluye una revisión histórica de las líneas de investigación, tanto teóricas como empíricas, publicadas sobre estructuras de hormigón reforzadas a flexión encolando materiales compuestos. El apartado III.3 se centra en el aspecto fundamental de la adherencia refuerzo-soporte. Se hace un repaso a distintos modelos propuestos para prevenir el despegue distinguiendo si éste se inicia en la zona de anclaje o si está inducido por fisuras en la zona interior del elemento. Se observa falta de consenso en las propuestas. Además en este punto se relatan las campañas experimentales publicadas acerca de la adherencia entre materiales compuestos y fábricas. En el apartado III.4 se analizan las particularidades de las estructuras de fábrica. Además, se revisan algunas de las investigaciones relativas a la mejora de su comportamiento a flexión mediante láminas de FRP. El comportamiento mecánico de muros reforzados solicitados a flexión pura (sin compresión) ha sido documentado por varios autores, si bien es una situación poco frecuente en fábricas reales. Ni el comportamiento mecánico de muros reforzados solicitados a flexocompresión ni la incidencia que el nivel de compresión soportado por la fábrica tiene sobre la capacidad resistente del elemento reforzado han sido suficientemente tratados. En cuanto a los trabajos teóricos, las diferentes propuestas se basan en los métodos utilizados para hormigón armado y comparten los principios habituales de cálculo. Sin embargo, presentan diferencias relativas, sobre todo, a tres aspectos: 1) la forma de modelar el comportamiento de la fábrica, 2) el valor de deformación de cálculo del refuerzo, y 3) el modo de fallo que se considera recomendable buscar con el diseño. A pesar de ello, el ajuste con la parte experimental de cada trabajo suele ser bueno debido a una enorme disparidad en las variables consideradas. Cada campaña presenta un modo de fallo característico y la formulación que se propone resulta apropiada para él. Parece necesario desarrollar un método de cálculo para fábricas flexocomprimidas reforzadas con FRP que pueda ser utilizado para todos los posibles fallos, tanto atribuibles a la lámina como a la fábrica. En el apartado III.4 se repasan algunas lesiones habituales en fábricas solicitadas a flexión y se recogen ejemplos de refuerzos con FRP para reparar o prevenir estos daños. Para mejorar el conocimiento sobre el tema, se llevan a cabo dos pequeñas campañas experimentales realizadas en el Instituto de Ciencias de la Construcción Eduardo Torroja. La primera acerca de la adherencia de materiales compuestos encolados a fábricas deterioradas (apartado IV.1) y la segunda sobre el comportamiento estructural a flexocompresión de probetas de fábrica reforzadas con estos materiales (apartado IV.2). En el capítulo V se analizan algunos de los modelos de adherencia propuestos para prevenir el despegue del extremo del refuerzo. Se confirma que las predicciones obtenidas con ellos resultan muy dispares. Se recopila una base de datos con los resultados experimentales de campañas sobre adherencia de FRP a fábricas extraídas de la literatura y de los resultados propios de la campaña descrita en el punto IV.1. Esta base de datos permite conocer cual de los métodos analizados resulta más adecuado para dimensionar el anclaje de láminas de FRP adheridas a fábricas. En el capítulo VI se propone un método para la comprobación en agotamiento de secciones de fábrica reforzadas con materiales compuestos sometidas a esfuerzos combinados de flexión y compresión. Está basado en el procedimiento de cálculo de la capacidad resistente de secciones de hormigón armado pero adaptado a las fábricas reforzadas. Para ello, se utiliza un diagrama de cálculo tensión deformación de la fábrica de tipo bilineal (acorde con el CTE DB SE-F) cuya simplicidad facilita el desarrollo de toda la formulación al tiempo que resulta adecuado para predecir la capacidad resistente a flexión tanto para fallos debidos al refuerzo como a la fábrica. Además se limita la deformación de cálculo del refuerzo teniendo en consideración ciertos aspectos que provocan que la lámina adherida no pueda desarrollar toda su resistencia, como el desprendimiento inducido por fisuras en el interior del elemento o el deterioro medioambiental. En concreto, se propone un “coeficiente reductor por adherencia” que se determina a partir de una base de datos con 68 resultados experimentales procedentes de publicaciones de varios autores y de los ensayos propios de la campaña descrita en el punto IV.2. También se revisa la formulación propuesta con ayuda de la base de datos. En el capítulo VII se estudia la incidencia de las principales variables, como el axil, la deformación de cálculo del refuerzo o su rigidez, en la capacidad final del elemento. Las conclusiones del trabajo realizado y las posibles líneas futuras de investigación se exponen en el capítulo VIII. ABSTRACT Strengthening of existing structures with externally bonded fiber reinforced polymers (FRP) has become the most common application of advanced composite materials in construction. These materials exhibit many advantages in comparison with traditional ones (corrosion resistance, light weight, easy to apply, etc.). But despite countless researches have been done, there are still doubts about some aspects of their behaviour and applications are carried out only with the help of guidelines, without official regulations. The aim of this work is to improve the knowledge on this retrofitting technique, particularly in regard to flexural strengthening of masonry structures. Reinforced concrete is often the strengthened material and external glued FRP plates are used to improve its flexural, shear or compressive (by wrapping) capacity. However the use of this technique on other materials like masonry structures looks promising. Unreinforced masonry is characterized for being a good material to support compressive stresses but really bad to withstand tensile ones. Glue composite plates can improve the flexural capacity of masonry elements subject to bending. But a proper bond between FRP sheet and masonry must be ensured to do that, especially in old buildings whose surface can be damaged due to being outside or ageing. The main objectives of the work and the methodology carried out are described In Chapter II. An extensive overview of the state of art is done in Chapter III. In Section III.1 physical and mechanical properties of fibers, matrix and composites and their main applications are related. Durability aspects are especially emphasized. Section III.2 includes an historical overview of theoretical and empirical researches on concrete structures strengthened gluing FRP plates to improve their flexural behaviour. Section III.3 focuses on the critical point of bonding between FRP and substrate. Some theoretical models to prevent debonding of FRP laminate are reviewed, it has made a distinction between models for detachment at the end of the plate or debonding in the intermediate zones due to the effects of cracks. It is observed a lack of agreement in the proposals. Some experimental studies on bonding between masonry and FRP are also related in this chapter. The particular characteristics of masonry structures are analyzed in Section III.4. Besides some empirical and theoretical investigations relative to improve their flexural capacity with FRP sheets are reviewed. The mechanical behaviour of strengthened walls subject to pure bending (without compression) has been established by several authors, but this is an unusual situation for real masonry. Neither mechanical behaviour of walls subject to bending and compression nor influence of axial load in the final capacity of the strengthened element are adequately studied. In regard to theoretical studies, the different proposals are based on reinforced concrete analytical methods and share common design principles. However, they present differences, especially, about three aspects: 1) the constitutive law of masonry, 2) the value of ultimate FRP strain and 3) the desirable failure mode that must be looked for. In spite of them, a good agreement between each experimental program and its theoretical study is often exhibited due to enormous disparity in considered test parameters. Each experimental program usually presents a characteristic failure mode and the proposed formulation results appropriate for this one. It seems necessary to develop a method for FRP strengthened walls subject to bending and compression enable for all failure modes (due to FRP or masonry). Some common damages in masonry subject to bending are explained in Section III.4. Examples of FRP strengthening to repair or prevent these damages are also written. Two small experimental programs are carried out in Eduardo Torroja Institute to improve the knowledge on this topic. The first one is concerned about the bond between FRP plates and damaged masonry (section IV.1) and the second one is related to the mechanical behaviour of the strengthened masonry specimens subject to out of plane bending combined with axial force (section IV.2). In the Chapter V some bond models to prevent the debonding at the FRP plate end are checked. It is confirmed that their predictions are so different. A pure-shear test database is compiled with results from the existing literature and others from the experimental program described in section IV.1. This database lets know which of the considered model is more suitable to design anchorage lengths of glued FRP to masonry. In the Chapter VI a method to check unreinforced masonry sections with external FRP strengthening subject to bending and compression to the ultimate limit state is proposed. This method is based on concrete reinforced one, but it is adapted to strengthened masonry. A bilinear constitutive law is used for masonry (according to CTE DB SE-F). Its simplicity helps to develop the model formulation and it has proven to be suitable to predict bending capacity either for FRP failures or masonry crushing. With regard to FRP, the design strain is limited. It is taken into account different aspects which cause the plate can’t reach its ultimate strength, like intermediate FRP debonding induced by opening cracking or environmental damage. A “bond factor” is proposed. It is obtained by means of an experimental bending test database that includes 68 results from the existing literature and from the experimental program described in section IV.2. The proposed formulation has also been checked with the help of bending database. The effects of the main parameters, like axial load, FRP design effective strain or FRP stiffness, on the bending capacity of the strengthened element are studied in Chapter VII. Finally, the main conclusions from the work carried out are summarized in Chapter VIII. Future lines of research to be explored are suggested as well.

Condicionantes de la adherencia y anclaje en el refuerzo de muros de fábrica con elementos de fibras

Es cada vez más frecuente la rehabilitación de patrimonio construido, tanto de obras deterioradas como para la adecuación de obras existentes a nuevos usos o solicitaciones. Se ha considerado el estudio del refuerzo de obras de fábrica ya que constituyen un importante número dentro del patrimonio tanto de edificación como de obra civil (sistemas de muros de carga o en estructuras principales porticadas de acero u hormigón empleándose las fábricas como cerramiento o distribución con elementos autoportantes). A la hora de reparar o reforzar una estructura es importante realizar un análisis de las deficiencias, caracterización mecánica del elemento y solicitaciones presentes o posibles; en el apartado 1.3 del presente trabajo se refieren acciones de rehabilitación cuando lo que se precisa no es refuerzo estructural, así como las técnicas tradicionales más habituales para refuerzo de fábricas que suelen clasificarse según se trate de refuerzos exteriores o interiores. En los últimos años se ha adoptado el sistema de refuerzo de FRP, tecnología con origen en los refuerzos de hormigón tanto de elementos a flexión como de soportes. Estos refuerzos pueden ser de láminas adheridas a la fábrica soporte (SM), o de barras incluidas en rozas lineales (NSM). La elección de un sistema u otro depende de la necesidad de refuerzo y tipo de solicitación predominante, del acceso para colocación y de la exigencia de impacto visual. Una de las mayores limitaciones de los sistemas de refuerzo por FRP es que no suele movilizarse la resistencia del material de refuerzo, produciéndose previamente fallo en la interfase con el soporte con el consecuente despegue o deslaminación; dichos fallos pueden tener un origen local y propagarse a partir de una discontinuidad, por lo que es preciso un tratamiento cuidadoso de la superficie soporte, o bien como consecuencia de una insuficiente longitud de anclaje para la transferencia de los esfuerzos en la interfase. Se considera imprescindible una caracterización mecánica del elemento a reforzar. Es por ello que el trabajo presenta en el capítulo 2 métodos de cálculo de la fábrica soporte de distintas normativas y también una formulación alternativa que tiene en cuenta la fábrica histórica ya que su caracterización suele ser más complicada por la heterogeneidad y falta de clasificación de sus materiales, especialmente de los morteros. Una vez conocidos los parámetros resistentes de la fábrica soporte es posible diseñar el refuerzo; hasta la fecha existe escasa normativa de refuerzos de FRP para muros de fábrica, consistente en un protocolo propuesto por la ACI 440 7R-10 que carece de mejoras por tipo de anclaje y aporta valores muy conservadores de la eficacia del refuerzo. Como se ha indicado, la problemática principal de los refuerzos de FRP en muros es el modo de fallo que impide un aprovechamiento óptimo de las propiedades del material. Recientemente se están realizando estudios con distintos métodos de anclaje para estos refuerzos, con lo que se incremente la capacidad última y se mantenga el soporte ligado al refuerzo tras la rotura. Junto con sistemas de anclajes por prolongación del refuerzo (tanto para láminas como para barras) se han ensayado anclajes con llaves de cortante, barras embebidas, o anclajes mecánicos de acero o incluso de FRP. Este texto resume, en el capítulo 4, algunas de las campañas experimentales llevadas a cabo entre los años 2000 y 2013 con distintos anclajes. Se observan los parámetros fundamentales para medir la eficacia del anclajes como son: el modo de fallo, el incremento de resistencia, y los desplazamientos que permite observar la ductilidad del refuerzo; estos datos se analizan en función de la variación de: tipo de refuerzo incluyéndose el tipo de fibra y sistema de colocación, y tipo de anclaje. Existen también parámetros de diseño de los propios anclajes. En el caso de barras embebidas se resumen en diámetro y material de la barra, acabado superficial, dimensiones y forma de la roza, tipo de adhesivo. En el caso de anclajes de FRP tipo pasador la caracterización incluye: tipo de fibra, sistema de fabricación del anclajes y diámetro del mismo, radio de expansión del abanico, espaciamiento longitudinal de anclajes, número de filas de anclajes, número de láminas del refuerzo, longitud adherida tras el anclaje; es compleja la sistematización de resultados de los autores de las campañas expuestas ya que algunos de estos parámetros varían impidiendo la comparación. El capítulo 5 presenta los ensayos empleados para estas campañas de anclajes, distinguiéndose entre ensayos de modo I, tipo tracción directa o arrancamiento, que servirían para sistemas NSM o para cuantificar la resistencia individual de anclajes tipo pasador; ensayos de modo II, tipo corte simple, que se asemeja más a las condiciones de trabajo de los refuerzos. El presente texto se realiza con objeto de abrir una posible investigación sobre los anclajes tipo pasador, considerándose que junto con los sistemas de barra embebida son los que permiten una mayor versatilidad de diseño para los refuerzos de FRP y siendo su eficacia aún difícil de aislar por el número de parámetros de diseño. Rehabilitation of built heritage is becoming increasingly frequent, including repair of damaged works and conditioning for a new use or higher loads. In this work it has been considered the study of masonry wall reinforcement, as most buildings and civil works have load bearing walls or at least infilled masonry walls in concrete and steel structures. Before repairing or reinforcing an structure, it is important to analyse its deficiencies, its mechanical properties and both existing and potential loads; chapter 1, section 4 includes the most common rehabilitation methods when structural reinforcement is not needed, as well as traditional reinforcement techniques (internal and external reinforcement) In the last years the FRP reinforcement system has been adopted for masonry walls. FRP materials for reinforcement were initially used for concrete pillars and beams. FRP reinforcement includes two main techniques: surface mounted laminates (SM) and near surface mounted bars (NSM); one of them may be more accurate according to the need for reinforcement and main load, accessibility for installation and aesthetic requirements. One of the main constraints of FRP systems is not reaching maximum load for material due to premature debonding failure, which can be caused by surface irregularities so surface preparation is necessary. But debonding (or delamination for SM techniques) can also be a consequence of insufficient anchorage length or stress concentration. In order to provide an accurate mechanical characterisation of walls, chapter 2 summarises the calculation methods included in guidelines as well as alternative formulations for old masonry walls as historic wall properties are more complicated to obtain due to heterogeneity and data gaps (specially for mortars). The next step is designing reinforcement system; to date there are scarce regulations for walls reinforcement with FRP: ACI 440 7R-10 includes a protocol without considering the potential benefits provided by anchorage devices and with conservative values for reinforcement efficiency. As noted above, the main problem of FRP masonry walls reinforcement is failure mode. Recently, some authors have performed studies with different anchorage systems, finding that these systems are able to delay or prevent debonding . Studies include the following anchorage systems: Overlap, embedded bars, shear keys, shear restraint and fiber anchors. Chapter 4 briefly describes several experimental works between years 2000 and 2013, concerning different anchorage systems. The main parameters that measure the anchorage efficiency are: failure mode, failure load increase, displacements (in order to evaluate the ductility of the system); all these data points strongly depend on: reinforcement system, FRP fibers, anchorage system, and also on the specific anchorage parameters. Specific anchorage parameters are a function of the anchorage system used. The embedded bar system have design variables which can be identified as: bar diameter and material, surface finish, groove dimensions, and adhesive. In FRP anchorages (spikes) a complete design characterisation should include: type of fiber, manufacturing process, diameter, fan orientation, anchor splay width, anchor longitudinal spacing and number or rows, number or FRP sheet plies, bonded length beyond anchorage devices,...the parameters considered differ from some authors to others, so the comparison of results is quite complicated. Chapter 5 includes the most common tests used in experimental investigations on bond-behaviour and anchorage characterisation: direct shear tests (with variations single-shear and double-shear), pullout tests and bending tests. Each of them may be used according to the data needed. The purpose of this text is to promote further investigation of anchor spikes, accepting that both FRP anchors and embedded bars are the most versatile anchorage systems of FRP reinforcement and considering that to date its efficiency cannot be evaluated as there are too many design uncertainties.

Some theoretical aspects in computational analysis of adhesive lap joints

This paper is devoted to the numerical analysis of bidimensional bonded lap joints. For this purpose, the stress singularities occurring at the intersections of the adherend-adhesive interfaces with the free edges are first investigated and a method for computing both the order and the intensity factor of these singularities is described briefly. After that, a simplified model, in which the adhesive domain is reduced to a line, is derived by using an asymptotic expansion method. Then, assuming that the assembly debonding is produced by a macro-crack propagation in the adhesive, the associated energy release rate is computed. Finally, a homogenization technique is used in order to take into account a preliminary adhesive damage consisting of periodic micro-cracks. Some numerical results are presented.

Use of Headed Reinforcement Bars in Contruction. A Theoretical Approach to Determine the Dimensions of Anchorage Plates and Experimental Tests on Knee Joints Subjected to a Closing Moment

In order to reduce costs and time while improving quality, durability and sustainability in structural concrete constructions, a widely used material nowadays, special care must be taken in some crucial phases of the project and execution, including the structure design and calculation, the dosage, dumping and curing of concrete: another important aspect is the proper design and execution of assembly plans and construction details. The framework, a name designating the whole reinforcement bars cage already assembled as shown in the drawings, can be made up of several components and implies higher or lower industrialization degree. The framework costs constitute about one third of the price per cubic meter placed in concrete works. The best solutions from all points of view are clearly those involving an easier processing to achieve the same goal, and consequently carrying a high degree of industrialization, meaning quality and safety in the work. This thesis aims to provide an indepth analysis of a relatively new type of anchoring by plate known as headed reinforcement bars, which can potentially replace standard or L-shaped hooks, improving the cleaning of construction details and enabling a faster, more flexible, and therefore a more economical assembly. A literature review on the topic and an overview of typical applications is provided, followed by some examples of specific applications in real projects. Since a strict theoretical formulation used to provide the design plate dimensions has not yet been put forward, an equation is proposed for the side-face blowout strength of the anchorage, based on the capacity of concrete to carry concentrated loads in cases in which no transverse reinforcement is provided. The correlation of the calculated ultimate load with experimental results available in the literature is given. Besides, the proposed formulation can be expanded to cases in which a certain development length is available: using a software for nonlinear finite element analysis oriented to the study of reinforced concrete, numerical tests on the bond-bearing interaction are performed. The thesis ends with a testing of eight corner joints subjected to a closing moment, held in the Structures Laboratory of the Polytechnic University of Madrid, aiming to check whether the design of such plates as stated is adequate for these elements and whether an element with plate-anchored reinforcement is equivalent to one with a traditional construction detail.

Beam Spectral Element with FRP Debonding

The behaviour of the interface between the FRP and the concrete is the key factor controlling debonding failures in FRP-strengthened RC structures. This defect can cause reductions in static strength, structural integrity and the change in the dynamic behavior of the structure. The adverse effect on the dynamic behavior of the defects can be utilized as an effective means for identifying and assessing both the location and size of debonding at its earliest stages. The presence of debonding changes the structural dynamic characteristics and might be traced in modal parameters, dynamic strain and wave patterns etc. Detection of minor local defects, as those origin of a future debonding, requires working at high frequencies so that the wavelength of the excited is small and sensitive enough to detect local damage. The development of a spectral element method gives a large potential in high-frequency structural modeling. In contrast to the conventional finite element, since inertial properties are modeled exactly few elements are necessary to capture very accurate solutions at the highest frequencies in large regions. A wide variety of spectral elements have been developed for structural members over finite and semi-infinite regions. The objective of this paper is to develop a Spectral Finite Element Model to efficiently capture the behavior of intermediate debonding of a FRP strengthened RC beam during wave-based diagnostics.

Muro cortina modular con marco de baja transmitancia térmica integrado en el vidrio aislante a través de adhesivos estructurales = Unitised curtain wall with low thermal transmittance frame integrated within the insulating glass unit through structural adhesives

Los muros cortina modulares están constituidos por paneles prefabricados que se fijan al edificio a través de anclajes a lo largo del borde del forjado. El proceso de prefabricación garantiza buena calidad y control de los acabados y el proceso de instalación es rápido y no requiere andamiaje. Por estas razones su uso está muy extendido en torres. Sin embargo, el diseño de los marcos de aluminio podría ser más eficiente si se aprovechara la rigidez de los vidrios para reducir la profundidad estructural de los montantes. Asimismo, se podrían reducir los puentes térmicos en las juntas si se sustituyeran los marcos por materiales de menor conductividad térmica que el aluminio. Esta investigación persigue desarrollar un muro cortina alternativo que reduzca la profundidad estructural, reduzca la transmisión térmica en las juntas y permita un acabado enrasado al interior, sin que sobresalgan los montantes. La idea consiste en conectar un marco de material compuesto de fibra de vidrio a lo largo del borde del vidrio aislante a través de adhesivos estructurales para así movilizar una acción estructural compuesta entre los dos vidrios y lograr una baja transmitancia térmica. El marco ha de estar integrado en la profundidad del vidrio aislante. En una primera fase se han efectuado cálculos estructurales y térmicos preliminares para evaluar las prestaciones a un nivel esquemático. Además, se han realizado ensayos a flexión en materiales compuestos de fibra de vidrio y ensayos a cortante en las conexiones adhesivas entre vidrio y material compuesto. Con la información obtenida se ha seleccionado el material del marco y del adhesivo y se han efectuado cambios sobre el diseño original. Los análisis numéricos finales demuestran una reducción de la profundidad estructural de un 80% y una reducción de la transmisión térmica de un 6% en comparación con un sistema convencional tomado como referencia. El sistema propuesto permite obtener acabados enrasados. ABSTRACT Unitised curtain wall systems consist of pre manufactured cladding panels which can be fitted to the building via pre fixed brackets along the edge of the floor slab. They are universally used for high rise buildings because the factory controlled assembly of units ensures high quality and allows fast installation without external access. However, its frame is structurally over-dimensioned because it is designed to carry the full structural load, failing to take advantage of potential composite contribution of glass. Subsequently, it is unnecessarily deep, occupying valuable space, and protrudes to the inside, causing visual disruption. Moreover, it is generally made of high thermal conductivity metal alloys, contributing to substantial thermal transmission at joints. This research aims to develop a novel frame-integrated unitised curtain wall system that will reduce thermal transmission at joints, reduce structural depth significantly and allow an inside flush finish. The idea is to adhesively bond a Fibre Reinforced Polymer (FRP) frame to the edge of the Insulated Glass Unit (IGU), thereby achieving composite structural behaviour and low thermal transmittance. The frame is to fit within the glazing cavity depth. Preliminary analytical structural and numerical thermal calculations are carried out to assess the performance of an initial schematic design. 4-point bending tests on GFRP and single-lap shear tests on bonded connections between GFRP and glass are performed to inform the frame and adhesive material selection process and to characterise these materials. Based on the preliminary calculations and experimental tests, some changes are put into effect to improve the performance of the system and mitigate potential issues. Structural and thermal numerical analysis carried out on the final detail design confirm a reduction of the structural depth to almost one fifth and a reduction of thermal transmission of 6% compared to a benchmark conventional system. A flush glazed appearance both to the inside and the outside are provided while keeping the full functionality of a unitised system.

Survey and correlation report on continuously reinforced pavements without joints, by W. H. Jacobs.

Mode of access: Internet.

Development of surface flaw thresholds for pre-cured fiber reinforced polymer and groove size tolerance for near surface mounted fiber reinforced polymer retrofit systems

Since the introduction of fiber reinforced polymers (FRP) for the repair and retrofit of concrete structures in the 1980’s, considerable research has been devoted to the feasibility of their application and predictive modeling of their performance. However, the effects of flaws present in the constitutive components and the practices in substrate preparation and treatment have not yet been thoroughly studied. This research aims at investigating the effect of surface preparation and treatment for the pre-cured FRP systems and the groove size tolerance for near surface mounted (NSM) FRP systems; and to set thresholds for guaranteed system performance. This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 10-59B to develop construction specifications and process control manual for repair and retrofit of concrete structures using bonded FRP systems. The research included both analytical and experimental components. The experimental program for the pre-cured FRP systems consisted of a total of twenty-four (24) reinforced concrete (RC) T-beams with various surface preparation parameters and surface flaws, including roughness, flatness, voids and cracks (cuts). For the NSM FRP systems, a total of twelve (12) additional RC T-beams were tested with different grooves sizes for FRP bars and strips. The analytical program included developing an elaborate nonlinear finite element model using the general purpose software ANSYS. The bond interface between FRP and concrete was modeled by a series of nonlinear springs. The model was validated against test data from the present study as well as those available from the literature. The model was subsequently used to extend the experimental range of parameters for surface flatness in pre-cured FRP systems and for groove size study in the NSM FRP systems. Test results, confirmed by further analyses, indicated that contrary to the general belief in the industry, the impact of surface roughness on the global performance of pre-cured FRP systems was negligible. The study also verified that threshold limits set for wet lay-up FRP systems can be extended to pre-cured systems. The study showed that larger surface voids and cracks (cuts) can adversely impact both the strength and ductility of pre-cured FRP systems. On the other hand, frequency (or spacing) of surface cracks (cuts) may only affect system ductility rather than its strength. Finally, within the range studied, groove size tolerance of ±1/8 in. does not appear to have an adverse effect on the performance of NSM FRP systems.